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I III-: AMI- [IIC AX XATUBALIST 



[Vol. LIV 



tended it by showing that anurans apparently first de- 

 velop solely as females and sexual intermediates, the 

 males only later differentiating from the females and 

 hermaphroditic forms. Moreover, these investigators 

 described in great detail modification of the sex ratios by 

 environmental changes such as extremes of temperature 

 and late fertilization. All of these alleged facts have 

 given rise to the belief that anurans in their sexual de- 

 velopment differ greatly from other vertebrates. 



For several years the writer has been engaged in 

 studying the germ cells of anurans, more especially Rana 

 catesbiana, with the object of testing the theories of sex 

 differentiation and development of the Pfliiger-Hertwig- 

 Kuschakewitsch school of German investigators. Al- 

 though at first inclined to admit their contentions, a more 

 careful survey of my material revealed several facts 

 irreconcilable with their views, but which could not be 

 satisfactorily interpreted. Fortunately an opportunity 

 presented itself of working with Professor E. G. Conklin 

 who suggested, after examining my material, that I was 

 probably dealing with a case of precocious ripening of 

 the germ cells in anuran larvae, i.e., condition stimulating 

 neoteny, using this word in the sense applied above. 

 The suggestion proved correct, and it is a pleasure to 

 acknowledge my indebtedness to Professor Conklin for 

 giving the clue to correct interpretation of the problem 

 and for many other helpful suggestions as well. The 

 present paper is a brief summary of a more extensive and 

 detailed investigation scheduled for later publication. 



In Rana ca lesbian a the larval period is very long, some 

 few individuals requiring four seasons to complete meta- 

 morphosis, though the usual period is about two years. 

 The sex of larvae 55-65 mm. in length is not difficult 

 to determine by examination of the gross structure of 

 the gonads, but if such superficial examination is supple- 

 mented by a hasty survey of the microscopic appearance 

 of the germ cells, then oddly enough hopeless confusion 

 of the sexes results, and what were apparently males 

 from macroscopic evidence turn out to be apparent fe- 



